1. Field of the Invention
The invention relates to a sound transmission apparatus and a sound transmission method, and particularly relates to a method and an apparatus for transmitting data using sound signals.
2. Description of Related Art
Frequency-shift keying (FSK) is a technique of transmitting data by using signals differing in frequency. FSK modulates carrier frequencies by using digital signals and realizes identification of signals and transmission of data through variation in frequency. Currently, the FSK technology transmits data by producing ultrasonic waves that are not perceivable by human ears by using a sound-producing array, so as to transmit data using sound signals at different sound frequencies.
For example, Table 1 below is a conventional correspondence table between the sound frequency signals and the characters. As shown in Table 1, when an apparatus A intends to transmit characters 1, 2, and 3 to an apparatus B, the apparatus A may convert the characters 1, 2, and 3 into basic tones 1, 2, and 3 based on Table 1 and sequentially transmits these basic tones to the apparatus B. When the apparatus B receives the basic tones, the apparatus B may convert the basic tones back to the characters 1, 2, 3 based on the definition in Table 1. Accordingly, data transmission is realized.
TABLE 1SoundFrequencySignalCharacterbasic tone 15Fbasic tone 14Ebasic tone 13Dbasic tone 12Cbasic tone 11Bbasic tone 10Abasic tone 99basic tone 88basic tone 77basic tone 66basic tone 55basic tone 44basic tone 33basic tone 22basic tone 11basic tone 00
However, in the data transmission above, each of the basic tones (at an independent sound frequency) only defines one character. Considering that the applicable sound frequency range is limited and the issue of the identification rate of the sound frequency signals, the basic tones that can be used in actual data transmission are quite limited. As a result, the amount of data (i.e., the number of characters) allowed to be transmitted at the same time is restricted, and the data transmission performance is thus influenced.